Structural System 2.ppt

8/16/2019 Structural System 2.ppt

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Structural SystemStructural S

ystem


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Factors Affecting Choice of StructuralSystems

The design should ensure a coordinated approach including

structure, envelope, services and finishes.

The principal decisions regarding structure relate to column

layout, foundation conditions, integration of building services,

and external wall construction.

The design of steel framed buildings encompasses not only the

structure, but also the building envelope, services and finishes.

ll these elements must be coordinated by a firm dimensional

discipline which recogni!es the modular nature of the

components to ensure maximum repetition and standardi!ations

in the predetermined grid layout.


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Types of Structural System"ollowings are the three types of Structural System#

Load-bearing wall construction

Skeleton framing

Combination of the two


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Factors Governing TypesFactors Governing Types

SelectionSelection

Economics $ not necessary the one that

requires the least structural materials

Architectural, Mechanical, Electrical

and other costs may be affected


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1. Load Bearing Walls

%oad &earing 'alls serves as#

Facades

Enclosures

Separators

Fire barriers

Carry oor ! roof loads

to the foundation


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Load-Bearing WoodLoad-Bearing Wood

Walls:Walls:

(ne to three storey buildings

)*ouses+

- x - or - x /- construction

Studs on 0/” to ” centers

Top 1 &ottom plates

*eaders

2ax. 'all ht. )3nsupported+ 4

05-


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Load-Bearing Masonry Walls:Load-Bearing Masonry Walls:

06 Storeys or 2ore

Thickness of 'alls vary depending on height

Trape!oidal cross section

%intels or arches at openings


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Load-BearingLoad-Bearing

reinforced concretereinforced concrete

Walls:Walls:

Thinner than 2asonry

Solid or 7avity

Load-Bearing WallsLoad-Bearing Walls

are used for:are used for:

8xterior

9nterior :artitions

'ind &racing

Service 7ore 8nclosure


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Load-Bearing Partitions:Load-Bearing Partitions:

Short inter"als

Carry Floor#Ceiling Loads

Load-Bearing walls:Load-Bearing walls:

Can ser"e as Shear $alls % &esists $ind !

Earth'uake (Seismic) Loads


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2. Skeleton Framing

Skeleton Framing serves

as:

7olumns carry "oundation

%ateral "orces resisted by

7olumns and ;iagonal &races, or


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Horizontal Structural Sla orHorizontal Structural Sla or

!eck:!eck:

"loor=7eiling=;ucts

"lat $ :late 7onstruction

"lat $ Slab reinforced concrete

Slab $ &and 7onstruction

Two 'ay Slabs


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Beam " #irder $onstruction:Beam " #irder $onstruction:

'ood >oist or


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Heavier Load % Longer S&ans:Heavier Load % Longer S&ans:

(ne $ 'ay


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Multi-Storey Medium

Span

Structures


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Multi-Storey Buildings W'y Multi-Storey Buildings are made(

%arge 3rban :opulation

8xpensive %and

o Multi-Storey Buildings make more e)cient use of land:

*igher the building )2ore Storeys + $ %arger the ratio of the building

"loor area to the used land area

o *ec'nological com&etition +very Hig' uildings,

o ntil t'e end of t'e ./t' century most uildings of

several storeys in t'e Western World were made of:

7ontinuous 'alls of brick or stone masonry supporting the roof

"loor from timber beams

o *'e same structural system used in t'e 0oman $ity of

Herculaneum


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Multi-Storey buildings beginningsMulti-Storey buildings beginnings Beginning of t'e .1t' century 2 forefront of

industrial revolution in 3ngland: ;emand for large factory buildings of several storeys and large clear

floor areas

7ast iron available in bulk 7ast iron columns used instead of bearing walls and cast iron beams in

stead of timber floor >oists.

3levator invented in S4 in ./567 enaling muc'

taller o)ce and a&artment uildings to e

constructed

Most multi-Storey uildings in S4 were still

making use of masonry walls instead of columns


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Forms of Multi-Storey Buildings"ollowings are the three "orms of 2ulti@Storey &uildings#

*+ on Continuous Columns with Continuous

.eams

/+ Continuous Multi-Storey Columns and

.eams

0+ Cross - $all Construction


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1. on !1. on ! "ontinuous"ontinuous "olumns and"olumns and

"ontinuous Beams#"ontinuous Beams#

Single Storey columns are >ointed at each floor level. :re@cast

edge beams or internal spine beams are erected over these

columns and are connected using high strength dowel bars in

grouted dowel tubes cast in the both the beams and columns.


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2. "ontinuous Multi-Storey "olumns

and Beams 2ulti@Storey 7olumns up to four storeys tall are commonly

used as perimeters columns with integrated corbel details.

"or buildings taller than four storeys, columns in two storey

lengths are used at higher levels with designed tie

connections at the column >oints. 7olumns can be

manufactured economically in the lengths of up to 0m.


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$. "ross ! Wall "onstruction 7ross $ 'alls 2ulti@Storey Structures consists of flooring and

%oad@&earing walls, where the walls support the floors and the

structure above. %ateral stability is provided transversely across

the building by the cross@wall system and longitudinally by stairs

and lift shaft cores, which are also formed by pre@cast wall

panels. This type of construction is ideal for buildings of cellular

structure, for example *otels, (ffice or partment &locks.


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Benefits 3naffected by the site weather conditions

7ompetitive :ricing

"actory :roduction to exacting quality standards

Speed of erection

8fficient and economic structure, based on earlier completion

period


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"ollowings are the Structural 8lements used in

2ulti@Storey &uilding# Columns

.eams

1lates

Arches

Shells

Catenaries

Structural Elements


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"olumns#

7olumns are elements that carry only axial force $ either

tension or compression $ or both axial force and bending

)which is technically called a beam@column but practically,

>ust a column+. The design of a column must check the axial

capacity of element and buckling capacity.


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Beams#A .eam may be2

7antilevered supported at one end only with a fixed connection

Simply supported )supported vertically at each end but able to rotate

at the supports+

7ontinuous )supported by three or more supports+

7ombination of the above )Supported at one end and in the middle+

&eams are elements which carry pure bending only. &ending

causes one section of a &eam )divided along its length+ to go into

compression and the other section into tension. The compression

section must be designed to resist buckling and crushing, while the

tension section must be able to adequately resist the tension.


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%lates# :lates carry bending in two directions. concrete flat slab is an

example of a plate. :lates are understood by using 7ontinuum

2echanics, but due to the complexity involved they are most

often designed using a codified empirical approach, or

computer analysis.

They can also be designed with yield line theory, where an

assumed collapse mechanism is analy!ed to give an upper

bound on the collapse load. This is rarely used in practice.


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S&ells# Shells derive their strength from their form and carry forces in

compression in two directions. dome is an example of Shell.

They can be designed by making a hanging@chain model, which

will act as a catenaryBs in pure tension and inverting the form to

achieve pure compression.


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Arches: rches carry forces in compression in one direction only

which is why, it is appropriate to build arches out of masonry.

They are designed by ensuring that the line of thrust of the

force remains within the depth of the arch.


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"atenaries# Catenaries derive their strength from their form and

carry transverse forces in pure tension by deflecting (just

as a tightrope will sag when someone walks on it). Theyare almost always cable or fabric structure. A fabric

structure acts as catenaries in two directions.


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Large Span StructureLarge Span Structure


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Structural Forms"ollowings are the structural "orms used for large

span structure#

.eam Structures

1ortals and Arches

Masted Structures

Space Frames

3mbrella Structures

Cable Structures


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Beam StructuresBeam Structures Structures consisting of beams supported on columns are simpleStructures consisting of beams supported on columns are simple

and commonly used, especially where the minimum internaland commonly used, especially where the minimum internal

volume is required.volume is required.


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%ortal and 'rc&es%ortal and 'rc&es

rches, which can take a variety of forms, are efficientstructures for long span roofs.


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Masted StructuresMasted Structures The concept of 2asted Structures is not new, but they have only

recently become popular as a means of providing lightweight

structures for general use.


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(mbrella Structures(mbrella Structures The final option for consideration is the umbrella or tree structures

in which the roof cantilevers from a central column and can be

repeated and >oined to other similar assemblies at each or any side

to form a continuous structures


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"able Structures"able Structures 7ables $ Aood resistance in tension, but no strength in compression

Tent# cable structure consisting of waterproofing membrane supported

by ropes or cables and posts

7able must be maintained in tension by pre@stressing in order to

avoid large vibrations under wind forces and avoid collapse


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"ables # )oof Structures"ables # )oof Structures 7ables in a cable $ supported roof

must be maintained in tension

easily achieved if the roof issaddle@shaped

Example:Example: *yperbolic paraboloid

with curvatures in opposite sense

in directions at right angleso 7ables hung in direction &;

o second set of cables placed

over them, parallel to direction

7 and put to tensiono 7ables from the second set press

down on those from the first one.

:utting them into tension as well #

"ully$tensioned network


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Example: (ne of the first doubly

curved saddle@shaped cable

supported roof was the ;orton

rena in


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"ables# Suspension Bridge"ables# Suspension Bridge Suspension &ridges#The simple design of early bridges#

7ables ) catenaries+

%ight deck

*angers suspending the deck on catenaries

%ack of stability in high winds

Gery flexible under concentrated loads, as the form of the cablewill adapt to loading form


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Example: 7apilano Suspension &ridge, 7anada.

7 ti


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7ontinue#

9mproved behavior under traffic and wind loads#

Stiffening trusses at the level of the deck that distributes

concentrated loads over greater lengths

lternatively# restrain vertical movement of the catenaries by

inclined cables attached to the top of the towers or below the deck


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Example:Example: The kashi@Haikyo &ridge, ?apan# 0DD0m spanThe kashi@Haikyo &ridge, ?apan# 0DD0m span


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Example: Aolden Aate &ridge, 7alifornia, 3S# 0I6m span


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Example: &rooklyn &ridge, 3S ) The largest from 0IIF until0D6F+# I/m span


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Famous Collapse:

Tacoma Carrows &ridge, 3S, collapsed on Covember E, 0D6due to wind@induced vibrations. 9t had been open for traffic for a

few months only before collapsing.


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"ables-Stayed Bridge"ables-Stayed Bridge cables@stayed &ridge consists of one or more piers, with cables

supporting the bridge deck

&asic idea# reduce the span of the beam )deck+ several times

compared to the clear span between the piers

Steel cable@stayed &ridges are regarded as the most economical

bridge design for the spans ranging between 66m and 66m

Shorter span# truss or box girder bridges

%arger spans# suspension bridges


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Example:


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Example: The 2illau Giaduct, "rance. %ongest span# Fm. Totallength# /6m.

Structural System 2.ppt

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